The present invention relates to a shaft seal, and more particularly to a packingless shaft seal.
In preparing a thermoplastic material for use in compression or injection molding, the ingredients of the plastic material are generally mixed together and then passed through an extruder to pelletize the plastic material. The extruder generally includes a shaft having a screw thread in its outer surface and rotatably supported in a housing. The thermoplastic material is fed to the shaft at the rear end of the screw thread and is forced along the screw thread to a pelletizing mechanism at the front end of the shaft. The rear end of the shaft is generally supported in a bearing having a seal which prevents the thermoplastic material from flowing rearwardly along the shaft. The shaft seal generally includes some type of packing material around the shaft. However, when extruding certain types of thermoplastic material, it was found that the extruded plastic material contained contaminating particles which were pieces of the packing material. Therefore, for extruding this type of thermoplastic material, it was found desirable to have an extruder which includes a packingless shaft seal which would not contaminate the plastic material but which would provide the desired sealing action.